1. Field of the Invention
The present invention relates to visual display apparatus, and particularly to visual projection apparatus for heads-up display of control information and graphics.
2. Background of the Invention
Devices which project visual information onto an opaque surface are well known. Familiar examples include motion picture projectors and projection television. Devices which protect visual information onto opaque, translucent, or transparent surfaces are also known. Examples of the latter include heads-up display systems for aircraft pilot. These devices permit critical information to be brought to the pilot's attention immediately with minimal distraction. Similar devices are also used in flight simulators employed in pilot training.
Examples of the latter are disclosed, for example, in U.S. Pat. Nos. 4,315,240, 4,315,241, 4,340,878, 4,347,507, 4,347,508, and 4,349,815 all assigned to Redifon Simulation Ltd. In the Redifon system such as disclosed, for example, in U.S. Pat. No. 4,315,240, a laser source, apparently a conventional continuous output gas laser, provides a laser beam which is split to provide two beams of equal intensity. Each beam is conditioned by passing through a modulator of conventional design which is controlled by a C.G.I. ("computer generated image") image generator. The output from the modulator is directed onto a polygonal rotating mirror which serves as a line scanner. A fiber optic light guide formed into a flat ribbon carries the scanned line from the line scanner to a frame scanning device which is mounted on the trainee's helmet. The line formed at the output end of the light guide is focused by a spherical lens onto the face of a rotating frame scanning mirror. When the mirror is stationary, emergent rays from the light guide are focused to form a single line of the computer generated image. As the mirror is rotated, successive lines of the image are projected to form an entire scanned image on a projection screen. The protected image simulates a view from the cockpit of an aircraft.
The projected image need not be visually continuous. Devices which project discrete elements of visual information such as alphanumeric characters are also known. For example, U.S. Pat. Nos. 4,241,343 and 4,099,172 disclose display devices which include a bank of light emitting diodes (LEDs) arranged in a row oriented in a common direction. A rotating optical element is provided to condition the light emitted by the LEDs to form a virtual image which is viewed by the observer. The rotating optical element which conditions the beams emerging from the LEDs can be a prism. The output of the LEDs is synchronized with the rotation of the optical element, and the LEDs are pulsed to form the image. The '172 patent also discloses an embodiment in which a plurality of plasma tubes are rotated to form a virtual image.
U.S. Pat. No. 4,109,832 discloses a device for projecting the image of a liquid crystal display onto an automobile windshield. This system employs reflected light during daylight hours and a weak, shadow-casting light source at night to provide the displayed image.
U.S. Pat. No. 4,439,755 provides a heads-up infinity display and pilot sight for projecting a reticle of weapon impact points, enhanced or computer processed data base images of the terrain over which the vehicle is passing and/or the like, without preventing the pilot from continuing to look out the windscreen of the aircraft.
U.S. Pat. No. 4,560,233 discloses an improved heads-up display, employing a cathode ray tube (CRT) having a penetron type of phosphor for providing a color display.
U.S. Pat. No. 4,427,977 discloses a video image display apparatus in which the scene displayed is determined by sensing the orientation of the viewing mechanism as controlled by user.
U.S. Pat. No. 4,575,722 discloses a heads-up magneto-optic display.
Despite the substantial advances which have been made in providing heads-up type displays for vehicle operators such as aircraft pilots and operators of vehicle simulators, there remains a substantial need for a simple visual display device which can be used to project real time information to vehicle operators such as automobile drivers. Similarly, there remains a substantial need for a simple, visual information display device which can be used to provide large scale displays of real time information which can be viewed simultaneously by a number of observers, such as plant operators situated in a control room of an electric utility generating plant, a manufacturing or chemical processing facility, or the like.